1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device obtaining a stable liquid crystal alignment, wide viewing angle in left and right directions, and high aperture ratio.
2. Discussion of the Related Art
With the development of the information society, demands for various display devices have increased. Accordingly, many efforts have been made to research and develop various flat display devices such as liquid crystal display (LCD), plasma display panel (PDP), electroluminescent display (ELD), and vacuum fluorescent display (VFD). Some types of the flat display devices are already applied to displays of various equipments.
Among the various flat display devices, the liquid crystal display (LCD) device has been most widely used due to advantageous characteristics of thinness, lightness in weight, and low power consumption. In many cases, the LCD device substitutes for Cathode Ray Tube (CRT). In addition to the mobile type LCD devices, such as a display for a notebook computer, LCD devices have been developed for computer monitors and televisions to receive and display broadcasting signals.
Despite various technical developments in the LCD technology with applications in different fields, research in enhancing the picture quality of the LCD device has been in some respects lacking as compared to other features and advantages of the LCD device. Therefore, in order to use the LCD device in various fields as a general display, the key to developing the LCD device lies on whether the LCD device can implement a high quality picture, such as high resolution and high luminance with a large-sized screen while still maintaining lightness in weight, thinness, and low power consumption.
The LCD device includes an LCD panel for displaying a picture image and a driving part for applying a driving signal to the LCD panel. The LCD panel includes lower and upper substrates bonded to each other at a predetermined interval, and a liquid crystal layer between the lower and upper substrates. The liquid crystal layer is driven by an electric field generated between the lower and upper substrates, thereby controlling a light transmittance by the liquid crystal layer. As a result, the picture image is displayed on the LCD panel.
Among the LCD devices, a Twisted Nematic (TN) mode LCD device has been most generally used. The TN mode LCD device has characteristics of varying the transmittance of light at each gray level in accordance with a corresponding viewing angle. Specifically, the transmittance of light is distributed symmetrically in right and left directions of the TN mode LCD device, but asymmetrically in lower and upper directions, whereby gray inversion is generated. In order to overcome such a problem, a method is proposed to compensate for the variation of light transmittance in accordance with a corresponding viewing angle by dividing a domain by differentiating an alignment direction of the liquid crystal layer in a pixel region.
A related art LCD device will be explained with reference to the accompanying drawings. FIG. 1 is a plan view illustrating a unit pixel of a related art LCD device, and FIG. 2 is a cross-sectional view taken along line I–I′ of FIG. 1.
The related art LCD device includes lower and upper substrates 1 and 10 facing each other, and a liquid crystal layer 16 between the lower and upper substrates 1 and 10.
The lower substrate 1 includes a plurality of gate and data lines 2 and 4 crossing another to define a plurality of pixel regions, a gate electrode 2a extended from both sides of the gate line 2, a gate insulating layer (not shown) on the lower substrate 1 including the gate line 2, an active region 3 on the gate insulating layer above the gate electrode 2a, a pixel electrode 7 in the pixel region at the same layer as the active region, a source electrode 4a extended from the data line 4 for being overlapped with one portion of the active region 3, a drain electrode 4b being apart from the source electrode 4a for being overlapped with another portion of the active region 3 and a predetermined portion of the pixel electrode 7, an interlayer passivation film 6 on an entire surface of the lower substrate including the pixel electrode 7, an alignment control electrode 5 on the interlayer passivation film 6 for being overlapped with the periphery of the pixel electrode 7, and a first alignment layer 8 on the lower substrate 1 including the alignment control electrode 5.
The upper substrate 10 includes a black matrix layer (not shown), a color filter layer (not shown) on the upper substrate 10 corresponding to the black matrix layer of the upper substrate 10 and the pixel regions of the lower substrate 1, a common electrode 13 on the color filter layer, the common electrode 13 having an X-shaped alignment control window 14, and a second alignment layer 15 on the upper substrate 10 including the common electrode 13. Then, the liquid crystal layer 16 is formed between the lower and upper substrates 1 and 10.
In the related art LCD device, when an electric field is generated between the pixel electrode 7 of the lower substrate 1 and the common electrode 13 of the upper substrate 10, as shown in an arrow of FIG. 2, a fringe field is generated by the alignment control window 14 inside the common electrode 13. Thus, liquid crystal molecules are differently aligned at both sides of the alignment control window 14 by the fringe field, thereby compensating a viewing angle.
However, the related art LCD device has the following disadvantages.
In the related art LCD device, the alignment control electrode 5 is formed of a metal material through which light does not pass, and the alignment control electrode 5 is spaced apart from the data line 4 by a predetermined interval to prevent a short between the alignment control electrode 5 from the data line 4 so that a width of the pixel region is decreased, thereby decreasing aperture ratio and luminance. In order to apply the related art LCD device to manufacturing, brightness of a backlight must be increased, whereby power consumption increases.
The aforementioned related art relates to a vertical alignment (VA) mode LCD device. In case of the TN mode LCD device, the electric field is generated such that the electric field faces outwardly in the periphery-of the pixel, so that the alignment of the liquid crystal is unstable. Accordingly, a light leakage is generated in the periphery of the pixel, thereby decreasing contrast ratio. Furthermore, the alignment of the liquid crystal becomes unstable even in a light touch, thereby generating a spot. Also, it is difficult to recover from the spot since a response time is slow.